1. Field of the Invention:
The invention relates to a process for the manufacture of aqueous solutions of anti-scaling agents, which show a high binding capacity, with respect to calcium and magnesium ions, and which can be advantageously used in the field of detergency.
2. The State of the Art
The action of the sequestering agents in the presence of drinking water, or of untreated industrial water, is well known; these agents, by formation of complexes with polivalent metal ions (for instance alkaline-earth metal ions, which form the water hardness) and even with other heavy ions, hinder the formation of precipitates, thus avoiding the scale (incrustation) deposition, in plants where water is warmed, such as boilers or heat-exchangers, the above mentioned agents hinder, as it is known, the scale formation on the metal surfaces. During home-washing and industrial cleaning, polivalent metal ions may interact with the anions present in the soil and with the anions coming from the detergent. In this case also the scaling (incrustation) action of the mentioned agents on the fabric fibers is known. When control agents are not present, the incrustation would increase the ash content, washing by washing, thus causing undesired matting and grey coloration phenomena.
A compound used for many years, showing an excellent activity against the formation of precipitates and inhibiting the re-deposition of solid particles and soil onto fabrics, is sodium tripolyphosphate. However, it is known that such compound, by degradation in water, gives rise to phosphates, which in turn favor the anomalous growth of algae in inland waters and seas, thus contributing to the phenomenon known as eutrofication and to the consequent reduction (in the most serious cases exhaustion) of the oxygen content in waters, with imaginable ecologic consequences. That is the reason for which in many countries, laws were introduced in order to limit or to forbid the use of sodium tripolyphosphate in detergents. Other coumpounds having a fair complexing and antiprecipitation activity against soil (and insoluble salts) are aminocarboxylic acids. For instance the sodium salts of nitrilotriacetic acid (NTA) and of ethylenediaminotetracetic acid (EDTA) can be mentioned. However, these compounds show some drawbacks, limiting their use, such as the presence of nitrogen in the molecule (nitrogen, in fact, has a role in the eutrofication process). Therefore, their use can be only a restricted use. The reduction of the Na tripolyphosphate contents in detergents has become possible by the use of gradually increasing amonts of Zeolite 4A (a particular sodium aluminosilicate) with substitution ratios higher that 1:1, on sodium tripolyphosphate. In order to get a more effective and complete activity of the detergent formulations having low phosphorus contents, the contemporary presence of other agents, different from zeolite, and/or detergency coadjuvants, showing a particular action, is also requested.
The Applicants have now found a new process for the manufacture of very effective products which do not contain phosphorus nor nitrogen atoms in their structure and which are consisting only of C, H and O atoms, exhibiting a fair effectiveness, so that they can be used as sequestering agents, or generally as coadjuvants, and furthermore as anti-scaling agents in processes involving the heating of drinkable and industrial waters. Furthermore, the new products can be used with great advantage in detergency processes, where the presence of alkaline earth ions, already in the cold, may give rise to the precipitation of insoluble salts, because of the interaction of some components of the detergent or as the result of heating processes, thus forming precipitates typical of the hard waters.
Said new products are aqueous solutions containing copolymers of maleic anhydride and of vinyl acetate, whose structure is simplified in formula (I): ##STR1## wherein X represents hydrogen and/or a monovalent cation, generally sodium, and wherein n is an index corresponding to the polymerization degree. The copolymer solutions according to the invention are showing quite higher technological properties, compared with the hydrolized or transesterified copolymers, described by British Patent 1385131 or respectively by Italian Patent 20015 A/89, which can be represented substantially by formula (II): ##STR2## wherein Y can mean: Na in the case of "hydrolized" copolymers;
H and/or CH.sub.3 (or another alkyl group) in the case of "transesterified" copolymers. PA1 (A) the amount of vinyl acetate ranges from 40 to 70% by moles (preferably 45-65%), with respect to the sum of all the comonomers, the amount of maleic anhydride ranges from 30 to 50% by moles, with respect to said sum, and the amount of termonomer ranges from 0 to 30% by moles (preferably from 1 to 10%), with respect to said sum, the molar ratio vinyl acetate/maleic anhydride being equal to or higher than 1; PA1 (B) maleic anhydride, vinyl acetate (and optionally said third monomer) are co-polymerized, optionally in the presence of a protective colloid, in an anhydrous reaction medium, consisting of an organic diluent having medium or low polarity; PA1 (C) the anhydrous suspension obtained according to (B), is directly subjected to a reactive extraction with water; PA1 (D) the organic phase is recycled, after separation of the phases, to stage (B) of the copolymerization; PA1 (E) the aqueous phase is optionally neutralized with an alkaline solution, for instance aqueous NaOH; afterwards it is directly transferred to storage or utilization.
The "hydrolized" copolymers, obtained by a drastic caustic treatment, retain, as is known, considerable amounts of sodium acetate, a by-product which is useless for the detergency purposes and which represents a weight loss in terms of active substance.
The "transesterified" copolymers do not contain any sodium acetate, but they require a complicated preparation process, based on operations which are not easy in the absence of water.